Internal combustion engines can operate with more than one fuel type, such as gasoline and compressed natural gas (CNG), for example. A multi-fuel engine may take advantage of the properties of each fuel type to improve emissions, mileage, power, etc. A multi-fuel engine may also be less expensive to operate as the costs of different fuels vary over time.
One class of multi-fuel engines operating with liquid and gaseous fuels provides a separate set of injection hardware for each fuel. In this way, it is possible to provide accurate injection control for each fuel type, and easily handle transitions between the different fuel types.
However, the inventors herein have recognized that while transitions between the different fuel types is relatively simple due to the duplicative hardware set-up, the transition may take a significant amount of time to effect. At one extreme, some engines stop combustion and engine rotation during the transition from one fuel type to another fuel type. Other engines may operate during the transition, but may suffer from poor emissions and increased risk of misfire. These difficulties may prevent the engine from taking full advantage of the properties of each fuel, since the cost of transitioning may exceed the savings of transitioning.
One approach to address the above issues includes an engine mounted in a vehicle with a fuel delivery system delivering gaseous fuel and liquid fuel to a fuel injector of a cylinder, such that the fuel injector inlet faces at least partially toward the road surface. The orientation of the fuel injector enables a quick transition from liquid fuel to gaseous fuel because the gaseous fuel can rise to the injectors and be preferentially injected. For example, injection of gaseous fuel by the fuel injector may begin even before the fuel rail is entirely purged of liquid fuel. In this way, it is possible to transition fuels with a reduced set of fuel injection hardware, and further improve combustibility during the transition. As such, it can be possible to enable more transitions as the engine encounters varied operating conditions. This is especially true when the engine is mounted in a vehicle, as the engine may cycle through many operating conditions as the vehicle accelerates, decelerates, and encounters varied terrain.
Furthermore, a complementary approach to address the above issues includes a method to control an engine with a fuel delivery system delivering liquid fuel to a first, direct, fuel injector of a cylinder and gaseous fuel and liquid fuel to a second fuel injector of the cylinder. The method comprises delivering liquid fuel to the first injector of the cylinder, selectively delivering liquid fuel to the second injector of the cylinder during a first condition, selectively delivering gaseous fuel to the second injector of the cylinder during a second condition, the second condition different than the first condition, and adjusting injection of the first injector when transitioning the second injector from liquid fuel to gaseous fuel and when transitioning the second injector from gaseous fuel to liquid fuel.
In this way, it is possible to compensate for the transition of fuel types in the second injector by adjusting operation of the first injector. For example, when transitioning the second injector from liquid to gaseous fuel, the injection of the second injector may cease and the injection of the first injector may be increased such that the amount of power generated by the engine is maintained entering the transition. The fuel delivery system feeding the second injector is transitioned from liquid fuel to gaseous fuel by stopping delivery of liquid fuel, starting delivery of gaseous fuel, and purging the second injector of liquid fuel with small injections by the second injector. The transition completes by decreasing injection of the first injector, resuming injection on the second injector, and completely purging the fuel rail of liquid fuel using the high pressure gaseous fuel to push liquid fuel past a float valve and through a pressure relief valve in the liquid fuel system.
As another example, when transitioning the second injector from gaseous to liquid fuel, the injection of the second injector may cease and the injection of the first injector may be increased such that the amount of power generated by the engine is maintained entering the transition. The fuel delivery system feeding the second injector is transitioned from gaseous fuel to liquid fuel by stopping delivery of gaseous fuel, starting delivery of liquid fuel, and purging the second injector of gaseous fuel with small injections by the second injector. The transition completes by decreasing injection of the first injector when resuming injection on the second injector.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.